Internally coated gun barrels



Aug- 4, 1970 B. D. wHlTLow 3,523,035

INTERNALLY COATED GUN BARRELS Filed Dec. 2l, 1966 I CO C12 (Q) @WHQL-91% HG. l I'IG. 2

/ l' l n 38 l" )i FIG. 5

56 )his United States Patent O1 iice 3,523,035 Patented Aug. 4, 1970 U.S. Cl. 117-97 4 Claims ABSTRACT F THE DISCLOSURE A barrel through which projectiles are to be fired comprised of a metal barrel shaped substrate upon at least the inner surface of which is coated a relatively thin layer of a dense, hard, wear and corrosion resistant vapor deposited material having a Mohs scale hardness of about 8 to 9. The coating is preferably titanium carbide having a duetile metal, such as cobalt, dispersed therein.

BACKGROUND 0F THE INVENTION Field of the invention This invention relates to metal working and, more particularly, to the making of guns or arms.

|Description of the prior art Many automatic weapons are limited in firepower by the material of which the barrel of the weapon is constructed. While a conventional machine gun can theoretically deliver many hundreds of rounds per minute, the weapon cannot as a practical matter deliver the theoretical firepower because the barrel would melt and/or become so distorted that accuracy would be lost and the operator endangered by the possibility of explosion of the barrel.

The operators are, therefore, limited to utilizing only short burst from the weapons, and even such short burst will quickly wear the barrel. In view of this rapid wear, gun crews commonly carry replacement barrels for their automatic weapons.

Also, with large eld pieces subjected to periods of continuous iring, it is necessary to periodically replace the barrel since even minimal wear can cause rounds to drop short of their intended target, which is usually several thousand yards from the iield place. The wear reduces accuracy and can endanger friendly troops.

No metal has yet been devised to provide a suitable solution to the wear and heat problems mentioned above.

SUMMARY OF THE INVENTION The invention may be generally described as a barrel through which projectiles may be fired which includes a metal substrate having the form of a barrel and a relatively thin, dense, hard, wear and corrosion resistant vapor deposited coating over at least the inner periphery of the substrate. The coating has a hardness from about 8 to 9 on the Mohs scale. The coated barrel has a much longer life than a conventional barrel assuring accuracy for longer periods and reducing the necessity for frequent replacement of barrels. Since the coating preferably used, titanium carbide having a duetile metal dispersed therein, has low thermal conductivity, the ybarrel will not become hot so quickly, reducing the distortion problem and permitting the firing of longer burst through the barrel.

Also, since the coating will sustain the Wear, lighter and less expensive metals may be used as a substrate than are conventionally used for barrels.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. l is a perspective view of a segment of the metal substrate of a gun barrel;

FIG. 2 is a perspective view of the segment illustrated in IFIG. 1 which has received a coating in accordance with the present invention;

FIG. 3 is an elevational view, in section, of an apparatus capable of applying the coating illustrated in FIG. 2;

FIG. 4 is an elevational view, in section, of a receptacle used in conjunction with the apparatus of FIG. 3; and

FIG. 5 is a perspective View of a barrel, partially cutaway to illustrate an alternative method of applying a coating.

DESCRIPTION OF THE PREFERRED EMBODIMENT In accordance with the present invention, and with reference to FIG. l, a gun barrel may be formed of a metal substrate 11, which is machined to form a cylindrical barrel and which may be provided with ril'ling, thus producing a plurality of grooves 12 along the interior of the barrel, as illustrated in FIG. 1.

The substrate 11 is coated with a relatively thin, dense, hard, wear and corrosion resistant coating 13 over the inner surface of the substrate 11, as illustrated in FIG. 2. The coating preferably employed is a titanium carbide coating having a duetile metal dispersed therein. Vapor deposited pure titanium carbide is quite brittle and lacks toughness, with the result that it exhibits inadequate resistance to shear forces and is, therefore, not preferred for use in the coating of the interior of the gun barrel. To impart toughness to the titanium carbide coating, a suitable ductile metal such as cobalt or nickel is simultaneously deposited with the titanium carbide upon the substrate. The dispersion that is formed is of the type in which titanium carbide is continuous phase and the d-uctile metal is the dispersed phase. In this type of dispersion, the ultra-hard characteristics of the pure titanium carbide are retained. Moreover, the dispersed particles of the duetile metal absorb energy, prevent high energy buildup from reaching the threshold energy density for fracture propagation and thereby function to stop the propagation of cracks which may originate in the titanium carbide matrix. Moreover, because of its greater coherence, such a dispersion strengthened material has considerably more impact resistance than ordinary titanium carbide.

Metal substrate 11 may be coated with a coating such as described above in an apparatus such as identified in FIGS. 3 and 4.

FIG. 3 illustrates a reactor 30 comprising a cylindrical body 33 surrounded by heating coil 34 and having two iitted end caps 38 and 36. End cap 38 has an exhaust outlet 37. End cap 36 mounted on top of the cylindrical body 33 has a reaction tube 41 found therein which extends into the central portion of the body 33. Reaction tube 41 has an integral at bottom wall 42 at its lower end which is provided with a plurality of recesses 43.

Recesses 143 receive therethrough plurality of gun barrels provided with threads 14 at their upper end which engage mating threads on annular collars .15. Collars serve to support the barrel 10 upon end wall 42 so that the multitudinal axis of the barrel 10 is substantially aligned with the multitudinal axis of the reactor 30. Body 33 and tube 41 form a flush chamber 44, dened between tube 41 and body 33. Tube `41 is appropriately tted with a cap 45 which carries a tube 46 extending therethrough and annularly down into the central portion of tube 41 to within one inch or so of the top of barrels 10. Receptacle 47 containing metal halide granules, cobalt chloride, for example, is suspended within the tube 46 (shown in greater detail in FIG. 4) at a point near the upper zone of the heating coils 34 surrounding the outside of cylinder 33. Heating coils controllably maintain the interior of the reactor 30 Within a temperature gradient of about 600 C. in the receptacle alone and about l000 C. in the deposition zone 60, as illustrated. Heating coils 34 may be either RF induction heaters, resistance heaters or any other suitable heating means for controllably maintaining the desired temperature in the zone of the receptacle 47 and the substrate or deposition zone 60.

A carrier gas stream of argon or helium gas is passed through the tube 46, carrying the metal halide vapor toward end wall `42, as shown in FIG. 3. Cap 45 is further provided With an inlet 48 through which titanium tetrachloride and carbon tetrachloride and a stream of hydrogen are introduced into tube 41 and passed downward outside the walls to the metal chloride tube 46. Upon reaching end wall 42, the metal chloride, titanium tetrachloride, carbon tetrachloride, hydrogen and cobalt chloride gases mix and pass downwardly to the interior 49 of the end barrels 10 where` the gases react to form coating 13 which comprises a deposit of ductile metal in titanium carbide. The reactions may be represented as:

End cap 36 is fitted with a flush inlet 51 through which a ush gas (argon, for example) is passed through the flush chamber 44. The flush gas entering inlet 49 passes through flush chamber 44 between the walls of cylinder 33 and tube 41 and downwardly around `barrels 10 to exit with bent reaction gases passing through barrels 10 through exhaust 37 provided in the lower end cap 38. The ush gas is used primarily to prevent contamination of the deposition zone 60 by back-drafts passing upwardly around the outside of barrels 10'.

In operation, purified helium or argon is first ushed through inlets 52, 48 and 51 to purge atmospheric gases from the reactor 30 in preparation for the deposition. When the reactor has been suciently purged, the flow of argon through tube 48 is stopped. Argon is introduced through tube 52 at the rate of approximately 35 cc./ min. The ow rate of argon (or helium) to tube 46 is varied according to the deposition rate of ductile metal desired. The chamber is then rapidly brought up to the operating temperature within the gradient previously given. Titanium tetrachloride and carbon tetrachloride are admitted to the reactor through feed tube 48, entrained in a carrier of hydrogen gas. This feed gas is prepared by bubbling hydrogen through bubbler bottles (not shown) containing the liquid titanium tetrachloride (TiCl4) and carbon tetrachloride (CCl4) at room temperature. The gas thus admitted through feed tube 48 is hydrogen saturated with TiCl4 and CCLL.

Upon reaching the interior of gun barrel 10, the hydrogen, titanium tetrachloride and carbon tetrachloride from tube 48 and the metal halide vapors from tube 46 mix and are simultaneously reduced by hydrogen gas into a mixture of titanium carbide and ductile metal which is deposited upon the substrate 11. The spent gas is passed downwardly through the bottom end of barrels 10 to exit with the ush gas through exhaust outlet 37.

A coating of from 1/2 to l mil in thickness is suitable for coating of a gun barrel, and only the surface of the barrel 10 which conventionally contacts the projectile need be coated as principal wear occurs on this surface. With the apparatus illustrated in FIGS. 3 and 4, only the inner surface of gun barrel will be coated as any gases which are unreacted will be swept from the outside of the gun barrel 10 by the inert gas flushed through flush chamber 44.

The time required to deposit a desired thickness of titanium carbide having cobalt dispersed therein will vary with the size of the substrate 11 and the flow rates of the reactants. With a specimen metal substrate, the following W rates:

Millimoles/min. TiCl4 1.342 CCI., 1.342 H2 1 122.000 CoCl2 0.029

the deposition rate was found to be .13 mil per hour. The titanium carbide coating having cobalt dispersed therein has Mohs scale hardness of between about 8 and 9, which is the preferred hardness. While cobalt is the desired ductile metal to be dispersed in the titanium carbide coating, it is to be understood that other ductile metals, such as nickel, for example, may be dispersed in titanium carbide by selection of the appropriate reactants, flow rates and temperatures. Moreover, it will be clear to one skilled in the art, after reading the above, that halides other than chloride may be employed. Indeed, various designed and types of reactors may be employed, it only being necessary to provide an apparatus capable of depositing a dense, hard, wear and corrosion resistant coating on the metal substrate, though a titanium carbide coating having cobalt dispersed therein is preferred.

Another method which can be employed to deposit the coating involves a reactor which may be formed of a cylindrical vessel, such as vessel 30, and having a heating coil like heating coil 34 therearound. However, instead of mixing the reactant gases at one end of the barrels 10, each reactant is introduced into the barrel separately through a perforate dip tube. To be specific, reference is made to FIG. 5. In FIG. 5, the barrel 10, which is supported within the heated zone of the reactor by any suitable means receives therethrough three small dip tubes 53-55. Each of tubes 53-55 are provided with a plurality of small apertures 56 throughout the length of the tube disposed between the ends of barrel 10. Into tube 53 is introduced a gaseous mixture of TiCl4 and H2, into tube 54 is introduced a gaseous mixture of CC14 and H2 and tube `55 carries a mixture of argon and gaseous CoCl2. Each of the three reactants are thus introduced through apertures `56 throughout the length of the barrel to assure that coating 13 is uniform throughout the length of the barrel.

I claim: 1. A barrel through which projectiles are to be red, comprising the combination of (a) a metal substrate having the form of a barrel;

and (b) a relatively thin, dense, hard, wearand corrosionresistant vapor deposited coacting comprising titanium carbide having a ductile metal selected from cobalt and nickel dispersed therein, said coating being applied over at least the inner surface of said substrate, and having a hardness from about 8 to 9 on the Mohs scale. 2. The article of claim 1, in which: the ductile metal dispersed in said titanium carbide is cobalt. 3. The article of claim 2, in which: said coating has a thickness of between 1/2 and l mil. 4. The article of claim 1, in which:

said coating is composed of a substantially continuous phase of titanium carbide having a cobalt phase dispersed therein and having a thickness between about 1/2 and '1 mil.

References Cited UNITED STATES PATENTS 3/1950 Brace et al. 5/1950 Germer et al 89-14 X RALPH S. KENDALL, Primary Examiner U.S. C1. X.R. 

